1. Field of the Invention
The present invention relates to an aircraft propulsion system, and particularly to an aircraft propulsion system which can secure the optimum thrust and thrust vector for flight conditions, as well as the optimum sectional area for the engine, and which is highly compatible with the environment.
2. Description of the Related Art
The optimum thrust, thrust vector, and sectional area for the engine are required in various flight conditions of an aircraft engine, such as take-off, cruise and landing conditions. For example, maximum thrust is required in a take-off condition, or thrust for increasing a direction of braking is required in a landing condition, whereas in a cruise condition are not required low air resistance. High bypass-ratio turbofan engines, which are used for many highly efficient civil aircraft engines, have large air inlet sectional area (engine sectional area), and do not require thrust during high-speed cruise as much as during take-off, thus the excessively large sectional area of the engine increases the resistance of the aircraft, resulting in a negative impact on the flight performances. For the purpose of simply increasing the thrust, an afterburner may be mounted in a rear portion of the engine to reduce the outer diameter of the fan, but actuation of the afterburner causes tremendous noise, and thus is not desirable in terms of the engine operation efficiency. As described above, with normal fixed engines, it is difficult to realize the optimum engine disposition and engine sectional area for all the flight conditions. However, it is of great benefit in aircraft traffic to deflect the thrust vector of aircraft engines, and the various ideas of the deflection have been proposed, thereby some of them are already in use. For example, Japanese Patent Application Laid-Open No. 2003-137192 (Title of the invention: “Vertical take-off and landing aircraft”, Date of laid-open publication: May 14, 2003) discloses a turbofan engine where thrust vector is made variable.
Among the systems, mechanisms of moving engines, or thrust vectoring nozzles for deflecting nozzles are beneficial for military-aircraft use where prompt change in thrust vector in aircraft traffic, but are not so beneficial for the use of civil aircraft the majority of which have large bodies. Civil aircraft require thrust vectoring particularly during take-off and landing. Examples of existing techniques for take-off conditions include a high-lift device which utilizes Coanda effect for the exhaust from the engine which is mounted below the wing by lowering the flap of a rear end of a wing in order to achieve increase of the lift force, and a method of achieving creation of lift force from deflection of the engine itself seen in a VTOL airplane, and of obtaining upward lift force by directing the fan upward during take-off, upon reception of air supplied by an air supply. However, these are not so economical in terms of their limited effects, and their mechanisms tend to be complex. On the other hand, using a thrust reverse to generate reverse thrust and reduce the braking distance when landing has been already carried out as a general matter. The fact is that the mechanism of generating reverse thrust has somewhat complex mechanisms.
Further, the recent environmental compatibility, that is less noise and lower amount of emission gas, is one of the most important issues regarding the performances of aircraft engines. The main reason why many aircraft engines employ high bypass-ratio turbofan engines is to achieve high efficiency and noise reduction. However, there is a limit to the development of aircraft engines which are improved year by year in terms of environmental compatibility, thus new ideas for engine systems are necessary in order to improve the basic performances. For example, for the direction required in the development of new engine systems, increasing bypass ratio by further expanding the diameter of the fan is necessary in terms of noise reduction, and electrical output through the engine is required in terms of lower amount of emission gas. Incidentally, Japanese Patent Application Laid-Open No. H11-200888 (Title of the invention: “Fuel cell turbine engine”, Date of laid-open publication: Jul. 27, 1999) discloses a fuel cell turbine engine which drives the motor by means of a fuel cell, drives the turbine by means of the motor, and drives the fan by means of output power of the turbine.
The problem in Japanese Patent Application Laid-Open No. 2003-137192 is that the turbofan engine with thrust vectoring mechanism is complex in terms of its mechanism, and the weight thereof is heavy.
Furthermore, the combination of a conventional electric motor and turbofan engine, or the fuel cell turbine engine disclosed in Japanese Patent Application Laid-Open No. H11-137192 has limited output, although it is compatible with the environment, thus the applicability to larger aircrafts is limited.